Conventionally, an air conditioner for a vehicle such as an electric vehicle, in which a heat source for a heating a passenger compartment is hardly secured, is known to heat air blown into a passenger compartment in a heat pump cycle (i.e., a vapor compression refrigerant cycle).
For example, Patent Document 1 and Patent Document 2 describe a heat pump cycle used for such kind of a vehicle air conditioner, in which a refrigerant cycle in a cooling operation and a refrigerant cycle in a heating operation are configured to be switchable. More specifically, in the heat pump cycle of Patent Document 1 and Patent Document 2, a refrigerant cycle is switched so that refrigerant absorbs heat from outside air at an exterior heat exchanger and releases the heat to air blown into a passenger compartment at an interior condenser, to heat the air blown into the passenger compartment in the heating operation.
In the heat pump cycle of Patent Document 2, in the heating operation, refrigerant is pressurized through multiple stages by two compression mechanisms such as a low stage compression mechanism and a high stage compression mechanism. An intermediate-pressure gas-phase refrigerant is mixed with a refrigerant discharged from the low stage compression mechanism, and the mixed refrigerant is drawn into the high stage compression mechanism. That is, a gas injection cycle (i.e., an economizer-type refrigerant cycle) is set to improve a coefficient of performance (COP) in the heating operation.